Angle Grinder: make it speed adjustable?

could i add something like a variable resistor of a dimmer switch into the cable of my grinder to be able to slow the speed down?

if so, or possibly, what tyoe of component? ideally small like an inline light-switch.

is there something about the type of motor used that would prevent it from working? ie it needs to run at a certain speed for example.

do have good qualtiy sanders, multitool, etc but there are still times when this would be handy, and i like to tinker with my power tools : )

it’s a 700w Makita.

ideas?

and i would of course like a cordless one, which do run quite a lot slower. it’s on the list. but in the mean time.

Bad idea…a grinding disc is designed to work under a specific speed and load, mess with both and it’s likley that the disc will fail.

wouldn’t be for cutting or grinding discs, but for wire brushes, pads etc

you realy think going slower would cause a disc to fail? i often give them pretty nasty tweaks, the thin ones, and they still hold up. quite hard to get them to fail achly.

and also then that would be problematic for the cordless grinders, right?

I find that as a rule of thumb, if you have to ask “can I screw about with mains electricity to…” then regardless of whether it’s actually possible, the sensible answer is invariably “no.”

Just buy a variable speed grinder?

https://www.boschtools.com/ca/en/boschtools-ocs/grind-rough-cuts-ag50-11vspd-46802-p/

Not in any way that I can think of.  Changing speed isn’t the same as changing brightness and you would normally need access to all of the terminals of the motor, not just the power cord.

Edit:let me modify that slightly. You might, depending on the sort of motor inside, get a sort of pseudo speed control where what you do is reduce the power so much that the motor ‘slips’ and you slow it down by loading the disk but it’s not really speed control and I’m not sure it’s giving you what you want

Probably not, AC motors spin at 50hz when unloaded (unless you wind them to spin at fractions of that) and any change from that has to be done in the gearbox.

You can change them over quite a narrow range by altering the power, lower the power and the motor ‘slips’ more as the rotor never catches up with the spinning field when loaded. But only by 10% or so.

Adjustable ones probably put the AC through a rectifier then a DC motor with speed control.

Screwfix do a cheap variable speed one, just get that.

Running at a lower speed = less cooling unless designed in the first page to be variable speed.

Lidl – Parkside do a 125mm variable speed angle grinder , others do them too – its not worth

trying to modify an existing tool.

Remember when you were a kid and you’d slow your bike down by sticking your foot between the tyre and the chain stay? Well you can vary the speed of the grinder by sticking your thumb between the disk and the guard 🙂

I’ve always thought a slower speed grinder would be good with Arbortech disks – partly for a bit more control over how much material they take off – as they can suddenly drag themselves into the wood and take out big bites of material –  but mainly so that the metal shurikens that start rebounding round the room then the disks fracture would be easier to dodge.

right thanks everyone. had a feeling that would be the case with the motor. makes sense.

to all the “just buy..” folk: the hwle point was not to just buy anything, more then perhaps a component that cost a tenner. and i won’t be buying parkside powertools thanks! but next time i replace my grinder i’ll look out for a variable speed one, sure.

thnaks for all the useful replies anyway

Nowt wrong with Parkside grinders.

Grinders are the one tool I buy cheap…. the cheaper ones are just a bit noisey

Incorrectly used slitting discs can fail quite spectacularly. However they are brilliant and on my cordless grinder they are brilliant for all manner of site jobs.

Phase fired SCR

Easy, plug it into a 110 volt supply, the yellow ones you find at building sites, should run at about half speed

should run at about half speed

not your best work really – is there nothing else catches your eye?

(ps. when I say ‘not your best work really’ – well, you understand…)